One known method for the input and output of light in optical fibers and planar optical waveguides is a method that is carried out with micromirrors. Micromirrors are inclined endfaces having an angle of, for example, 45 degrees so as to change the light path 90 degrees.
In a known method of forming such mirrors, the inclined endfaces are formed by cutting into an optical waveguide with a dicing blade.
For example, Patent Document 1 below describes carrying out a cutting operation in which a dicing blade equipped with a cutting edge having an apex angle of 90°, or a one-sided cutting edge having a substantially wedge-shaped cross-section with an apex angle of 45°, is applied perpendicular to the optical waveguide. By means of such a cutting operation, a V-shaped groove is formed in the optical waveguide, thereby forming a micromirror having an inclined plane in cross-section. It is also mentioned that a micromirror formed in this way emits the light that propagates through the optical waveguide outside the plane of the waveguide, or causes the optical path of light that enters from outside the plane of the optical waveguide to be coupled to the optical waveguide. However, when a method of cutting into an optical waveguide with a dicing blade like that disclosed in Patent Document 1 is used, because the mirror face is formed by a cutting operation following formation and curing of the optical waveguide, cutting debris remains around the optical waveguide, which may cause optical loss to arise.
Patent Document 2 below discloses a process wherein a stamper on which has been formed a raised pattern corresponding to a core shape is pressed against a liquid photocurable resin for cladding formation, following which the pressed face is irradiated with ultraviolet light from the opposite side to form a core groove. A core is then formed by filling the resulting core groove with a liquid core material. With such a method, by forming mirror shapes on the stamper, it is possible to form mirror faces. However, in cases like that disclosed in Patent Document 2 where a stamper on which a raised pattern has been formed is pressed into a liquid photocurable resin for cladding formation, because liquid photocurable resin in unexposed areas sticks to the surface of the stamper pattern each time pressing is carried out, the surface must be cleaned after each pressing operation, which makes the process cumbersome. Another problem has been that, in a method where a core groove having a mirror shape is created then is filled with resin, shadowing of the mirror face occurs, making it difficult to form a reflective film on the mirror face. Also, in a method where the core is formed by filling a core groove with resin and curing the resin, shrinkage that arises during curing of the resin subjects the mirror face to shear strain, which tends to lead to peeling of the reflective film. In addition, because a resin varnish is used to fill a groove several tens of micrometers in depth with resin, vaporization of the solvent has a deleterious effect on the environment at the manufacturing site. Moreover, a thin film of the core material having a high refractive index sometimes remains on the surface of the cladding, as a result of which light leakage may arise from such places. Finally, because the stamper pattern must be provided with a taper in order to lower the release resistance, it has only been possible to create cores having cross-sectional shapes that are trapezoidal. In such cases, the coupling loss to light-emitting devices, light-receiving devices, fibers and the like increases.
Patent Document 3 discloses a method of forming a mirror face by driving a working head having a face which intersects the leading end of the working head at an angle of 45 degrees into a light-guiding sheet composed of a thermoplastic resin or a thermoset resin. However, a method like that disclosed in Patent Document 3 is problematic in that the impact when driving in the working head may cause cracks to form in the optical waveguide and the shaped face tends not to be smooth.